A cheap non sine wave inverter works fine, no need for a more expensive pure sine wave. I use a Harbor Freight piece of crap, rated at 700 watts, continuous. You will need to upgrade your existing 12 VDC outlet, get a real good quality one, marine catalogs are good for this. Go right to your battery, with 10 gauge 2 conductor stranded wire (any big truck supply house will sell this by the foot, and it has a tough outer jacket kind of like Romex, but is UV resistant, DO NOT USE ROMEX) use a fuse, you will pull more amps then the stock outlets can handle and if you try it you will just blow fuses, use a bigger fuse and you will fry wiring. You need a whole separate outlet to do it right. I use a 30 amp fuse, and pull about 22 amps (as I recall) when charging my 52 VDC battery at 3 amps.
To really do it right, get a Prius, then you can just leave the car "on" (engine will be off) and walk away, go eat lunch, whatever. The main traction battery (I have a plug in Prius, but the regular ones work the same way) keeps the 12 volt acc. battery topped off, and eventually when the big battery gets low, the car auto starts, runs a few minutes (and at an extremely efficient fuel burn rate, nothing like a regular car sitting there idling) and then shuts off again. I've taken multi day trips and never turned the car off, a Prius and a ebike is a great combo. If you're not into that type of work, take your car to any competent car stereo installer, along with your heavy duty 12 VDC marine outlet, and they can knock it out in an hour or so, piece of cake.
